Align vertices along vector (Python)
Unit direction vector. 

Suggest doing this without the transform matrix. The direction vector

&gt;&gt;&gt; d = Vector((1, -1, 0))


can be normalized, ie have a length of one, to 

&gt;&gt;&gt; d.normalize() # in place normalize
Vector((0.7071067690849304, -0.7071067690849304, 0.0))


Now, given a source location point p can move from p x units in the direction d using

new_loc = p + x * d  # x is a scalar.


In the context of your original question

import bpy
import bmesh
from mathutils import Vector

me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)

p = Vector() # using origin as source point.

vec = Vector((1, -1, 0))  # direction vector
d = vec.normalized()  # unit direction vector

newverts = [bm.verts.new(p + x * d) for x in (1, 1.5, 2)]

bmesh.update_edit_mesh(me)